{"id":"CVE-2026-5388","title":"justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge …","summary":"justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge …","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-20"],"vendor":"justhtml","product":"justhtml","affected":["justhtml < 1.15.0"],"patched":["justhtml 1.15.0"],"published":"2026-08-23","updated":"2026-10-12","sourceUpdated":"2026-10-12T16:10:00.220","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-5388","references":[{"url":"https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-c9vm-hv86-f23r","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/justhtml-before-multiple-security-issues","label":"disclosure@vulncheck.com"},{"url":"https://github.com/EmilStenstrom/justhtml"},{"url":"https://github.com/EmilStenstrom/justhtml/compare/v1.14.0...v1.15.0"},{"url":"https://github.com/EmilStenstrom/justhtml/releases/tag/v1.15.0"}],"tags":["nvd","osv","pip"],"epss":0.00587,"epssPercentile":0.47876,"aliases":["GHSA-c9vm-hv86-f23r"],"ecosystem":"pip","ingestedAt":"2026-08-24T19:25:44.153Z","slug":"CVE-2026-5388","body":"## Overview\n\njusthtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript — for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw </textarea> reintroduction through Markdown passthrough, or preserved <style>/<meta http-equiv=refresh>/<base href> tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Package advisory (CVE-2026-5388)\n\nAffected packages:\n\n- `justhtml < 1.15.0`\n\nPatched in:\n\n- `justhtml 1.15.0`\n\nSource: https://osv.dev/vulnerability/GHSA-c9vm-hv86-f23r","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":219482,"id":"CVE-2026-5388","ts":1791824359773,"field":"cvss","old":null,"new":"9.8"},{"seq":219481,"id":"CVE-2026-5388","ts":1791824359773,"field":"severity","old":"medium","new":"critical"}]}